IR spectroscopy measurements may be useful for a variety of purposes including aerospace, automotive and industrial applications, as well as biological and bio-medical applications. For example, infrared (IR) radiation is readily absorbed by materials in association with relative motions (vibrations) of atoms such as carbon, hydrogen, oxygen and nitrogen. As such, IR spectroscopy measurements may indicate a condition of a wide variety of organic as well as inorganic materials.
For example, frequently it is necessary to determine the thickness of a coating material on a substrate, to verify that the film coating thickness is sufficiently thick, but not too thick, including but not limited to, bond primer film thicknesses on a metallic substrate. It is frequently necessary to measure surfaces that are the inner walls of a tube or fitting and for that a flexible fiber optic measurement is needed. Near-IR spectrometers generally work well with fiber optic probes
One problem with determining the thickness of thin films on substrates may include the fact that the surface may include surface roughness, making surface contact methods that contact the surface over the scale of the roughness, such as eddy current measurement methods, inadequate. In addition, the film may be sufficiently thin to make prior art methods such as eddy current detection and ultrasound methods inadequate.
Other infrared(IR) non-destructive methods in the prior art used to measure the properties of thin films include using IR absorbance to determine the amount of a chromated conversion coating on a metallic substrate (U.S. Pat. No. 6,794,631), determining the amount of an anodize coating on a metallic substrate, (U.S. Pat. No. 6,784,431), determining an amount of chemical cure and amount of surface contamination (U.S. Pat. No. 6,906,327), determining the amount/thickness of an opaque coating on a substrate (U.S. Pat. No. 6,903,339) and (U.S. Pat. No. 7,223,977), and determining an amount of heat damage to a resin-fiber composite substrate (U.S. Pat. No. 7,115,869), all of which are fully incorporated by reference herein.
None of the above methods and associated devices, however, disclose a method or device that is suitable for performing IR spectroscopy including determining a thickness of a film coating on a substrate, particularly where a portable, real-time capability is desirable, and the inner surfaces of a tube or fitting needs to be measured, such as in aircraft manufacturing, assembly, maintenance, and repair of aircraft.
Thus, there is a continuing need for improved IR non-destructive testing methods including a method that is suitable for performing IR spectroscopy to determine a thickness of a film coating on a substrate, including a portable, real-time near-IR spectroscopic method with a flexible fiber optic probe, advantageously usable in aircraft manufacturing, assembly, maintenance, and repair of aircraft.
Therefore it is an object of the invention to provide a method that is suitable for performing IR spectroscopy to determine a thickness of a film coating on a substrate, including a portable, real-time near-IR spectroscopic method with a flexible fiber optic probe, advantageously usable in aircraft manufacturing, assembly, maintenance, and repair of aircraft.